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Table Of Contents  The TCP/IP Guide
 9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)
      9  TCP/IP Network Configuration and Management Protocols (BOOTP, DHCP, SNMP and RMON)
           9  Host Configuration and TCP/IP Host Configuration Protocols (BOOTP and DHCP)
                9  TCP/IP Dynamic Host Configuration Protocol (DHCP)
                     9  DHCP Configuration and Operation

Previous Topic/Section
DHCP General Operation and Client Finite State Machine
Previous Page
Pages in Current Topic/Section
12
3
Next Page
DHCP Lease Reallocation Process
Next Topic/Section

DHCP Lease Allocation Process
(Page 3 of 3)

Dealing With Lost Messages or Failure of the Allocation Process

You can see in this description that there are a number of situations that may occur that require a client to retransmit messages. This is because DHCP uses UDP which is unreliable and can cause messages to be lost. If retransmissions don't fix a problem such as not receiving a DHCPOFFER or a DHCPACK from a server, the client may have to start the allocation process over from scratch. The client must include enough “intelligence” to prevent it from simply trying forever to get a lease when there may not be a point—for example, if there are no DHCP servers on the network, no number of retransmissions will help.

Thus, after a number of retries the client will give up and the allocation process will fail. If the client is configured to use the Automatic Private IP Addressing feature, this is where it would be used to give the client a default address. Otherwise, the client will be, well, “dead in the water”.

Key Concept: The most important configuration process in DHCP is the lease allocation process, used by clients to acquire a lease. The client broadcasts a request to determine if any DHCP servers can hear it. Each DHCP server that is willing to grant the client a lease sends it an offer. The client selects the lease it prefers and sends a response to all servers telling them its choice. The selected server then sends the client its lease information.



Previous Topic/Section
DHCP General Operation and Client Finite State Machine
Previous Page
Pages in Current Topic/Section
12
3
Next Page
DHCP Lease Reallocation Process
Next Topic/Section

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